The invention relates to a LED lamp comprising a gear column, a lamp cap which is connected to an end of the gear column and a substrate which is connected to the other end of the gear column and which is provided with a number of LEDs.
Such a LED (Light Emitting Diode) lamp is known from English patent publication GB 2,239,306, which more particularly describes a LED lamp which can suitably be used for decorative purposes. The known lamp comprises a customary base with a BC cap or a continental screw cap, a gear column which accommodates the electronic gear necessary to operate the LEDs, as well as a substrate which is circularly symmetrical when viewed in the direction of the longitudinal axis of the lamp, in which substrate a number of individual LEDs are incorporated. The colors generated by the different LEDs during operation of the lamp may differ. By using an adjustable switching time control, it is possible to generate specific lighting effects and lighting patterns with the known lamp.
The known lamp has a number of drawbacks. One of these drawbacks is that the lamp can only be used for signaling purposes, whereby the LEDs of the lamp draw attention via a specific adjustable flashing frequency. The known lamp cannot provide for continuous, uniform lighting with a high luminous flux. In addition, the manufacture of the known lamp is relatively complicated. This applies in particular if the known lamp must be provided with a large number of LEDs.
It is an object of the invention to obviate the above-mentioned drawback. The invention more particularly aims at providing a LED lamp which can be relatively easily mass-produced, and which can be operated such that continuous, uniform lighting with a high luminous flux is obtained.
These and other objects of the invention are achieved by a LED lamp of the type mentioned in the opening paragraph, which is characterized in that the substrate comprises a regular polyhedron of at least four faces, whereby faces of the polyhedron are provided with at least one LED which, during operation of the lamp, has a luminous flux of at least 5 lm, and the gear column is provided with heat-dissipating means which interconnect the substrate and the lamp cap.
The invented lamp enables continuous, uniform, high-intensity lighting to be achieved. It has been found that LEDs having a luminous flux of 5 lm or more can only be efficiently used if the lamp comprises heat-dissipating means. Customary incandescent lamps can only be replaced by LED lamps which are provided with LEDs having such a high luminous flux. A particular aspect of the invention resides in that the heat-dissipating means remove the heat, generated during operation of the lamp, from the substrate via the gear column to the lamp cap and the mains supply connected thereto.
The use of a substrate which is composed of a regular polyhedron of at least four faces enables the intended uniform lighting to be achieved. The regular polyhedron is connected to the gear column, preferably, via a vertex. However, the polyhedron may in principle also be connected to the gear column in the center of one of the faces. The greatest uniformity in lighting is obtained if each one of the faces is provided with the same number of LEDs of the same type.
In experiments leading to the present invention, it has been found that favorable results can be achieved with polyhedrons in the form of an octahedron (regular polyhedron of eight faces) and dodecahedron (regular polyhedron of twelve faces). Better results, however, are achieved with substrates in the form of a hexahedron (polyhedron of six faces, cube). In practice it has been found that a good uniformity in light distribution can already be obtained using substrates in the form of a tetrahedron (regular polyhedron of four faces, pyramid). In an alternative embodiment the substrate comprises a three-dimensional body like a sphere or an ellipsoid, or a pat of a sphere or an ellipsoid.
A favorable embodiment of the LED lamp is characterized in that the lamp is also provided with a (semi-)transparent envelope. This envelope may be made of glass, but is preferably made of a synthetic resin. The envelope serves as a mechanical protection for the LEDs. In addition, the envelope may contribute to obtaining the uniform lighting which can be obtained with the lamp.
A further interesting embodiment of the LED lamp is characterized in that the heat-dissipating means comprise a metal connection between the substrate and the lamp cap. It has been found that such a connection, which may preferably consist of a layer of copper, properly dissipates the heat from the substrate to the lamp cap. In principle, the gear column may entirely consist of a heat-conducting material, for example a metal such as copper or a copper alloy. In this case, it must be ensured that the electronics present in the gear column is properly electrically insulated from the metal gear column. Preferably, also the substrate is made of a metal, such as copper or a copper alloy.
Yet another embodiment of the LED lamp is characterized in that means are incorporated in the column, which are used to generate an air flow in the lamp. Such means, preferably in the form of a fan, can be used, during operation of the lamp, to generate forced air cooling. In combination with the heat-dissipating means, this measure enables good heat dissipation from the gear column and the substrate.
A further embodiment of the invented LED lamp is characterized in that the faces of the polyhedron are provided with an array of LEDs, which preferably comprises at least one green, at least one red and at least one blue LED or at least one green, at least one red, at least one yellow and at least one blue LED or at least one white LED. By virtue of the shape of the substrate, such an array of LEDs can be readily provided, often as a separate LED array, on the faces of the substrate. This applies in particular when the faces of the polyhedral substrate are substantially flat. Such a LED array generally comprises a number of LEDs which are provided on a flat printed circuit board (PCB). In practice, LEDs cannot be readily secured to a substrate which is not level. If LEDs with a high luminous flux (5 lm or more) are used, then a so-called metal-core PCB is customarily used. Such PCBs have a relatively high heat conduction. By providing these PCBs on the (preferably metal) substrate by means of a heat-conducting adhesive, a very good heat dissipation from the LED arrays to the gear column is obtained.
By using one or more LED combinations in the colors green, red and blue or green, red, yellow and blue for each substrate face, a LED lamp can be obtained which emits white light. Such LED combinations composed of three different LEDs are preferably provided with a secondary optical system, in which the above-mentioned colors are blended so as to obtain white light. Another interesting embodiment of the LED lamp is characterized in that the lamp is provided with means for changing the luminous flux of the LEDs. If the gear column is provided with electronics suitable for this purpose, then this measure enables a dimmable LED lamp to be obtained. The dim function is preferably activated by means of an adjusting ring which is attached to the gear column at the location of the lamp cap. It is obvious that, if an envelope is used in the lamp, the adjusting ring must be situated outside the envelope.
A further interesting embodiment of the invented LED lamp is characterized in that the lamp is provided with means for mutually varying the luminous flux of the LEDs provided on the various faces of the substrate. The electronics necessary for this function is incorporated in the gear column of the lamp. By using this measure, it is possible to change the spatial light distribution of the LED lamp. If LEDs of different colors are used, it is also possible to adjust the color and the color distribution of the LED lamp. The distribution of the color and/or light distribution is preferably adjusted via an adjusting ring, which is connected to the gear column at the location of the lamp cap. It is obvious that, if an envelope is used in the lamp, the adjusting ring must be situated outside the envelope.